providing DSResponses that make use of data from two or more DataSources, by sending
DSRequests to those other DataSources, waiting for both to respond, then combining the
response data (note that for something like a SQL join, you should instead use
DataSourceField.includeFrom if you have Smart GWT Pro or better)

This facade pattern can be implemented either server-side or client-side:

server-side (Smart GWT Pro or better), implement a custom DataSource (see QuickStart
Guide) and implement the server-side API DataSource.execute() by calling
DataSource.execute() on some other DataSource, then return the DSResponse that results.

client-side, use dataProtocol:"clientCustom". The
FacadeDataSource provides a specific implementation that is
useful for testing
purposes. Alternative, the code below shows the simplest possible code for the facade
pattern when implemented client-side via dataProtocol:"clientCustom" - requests
are forwarded to another DataSource, and the responses are returned completely unchanged.